Messages in this thread Patch in this message | | | Date | Tue, 23 Mar 2010 21:20:53 -0400 | From | Mathieu Desnoyers <> | Subject | Re: 2.6.33 GP fault only when built with tracing |
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* Randy Dunlap (randy.dunlap@oracle.com) wrote: > On Fri, 19 Mar 2010 14:46:10 -0400 Mathieu Desnoyers wrote: > > > * Randy Dunlap (randy.dunlap@oracle.com) wrote: > > > On 03/18/10 17:59, Mathieu Desnoyers wrote: > > > > * Steven Rostedt (rostedt@goodmis.org) wrote: > > > >> On Thu, 2010-03-18 at 16:26 -0700, Randy Dunlap wrote: > > > >>> I can build/boot 2.6.33 with CONFIG_TRACE/TRACING disabled successfully, > > > >>> but when I enable lots of tracing config options and then boot with > > > >>> ftrace=nop on the kernel command line, I see a GP fault when the parport & > > > >>> parport_pc modules are loading/initializing. > > > >> > > > >> Do you see it without adding the "ftrace=nop"? The only thing that > > > >> should do is expand the ring buffer on boot up. > > > >> > > > >>> > > > >>> It happens in drivers/parport/share.c::parport_register_device(), when that > > > >>> function calls try_module_get(). > > > >>> > > > >>> If I comment out the trace_module_get() calls in include/linux/module.h, > > > >>> the kernel boots with no problems. > > > >> > > > >> > > > >> Interesting. Well, trace_module_get() is a TRACE_EVENT tracepoint. But > > > >> should be disabled here. It may be something to do with DEFINE_TRACE. > > > >> > > > >> (added Mathieu to Cc since he wrote that code) > > > > > > > > can you try replacing the "local_read(__module_ref_addr(module, cpu))" argument > > > > with "0" ? > > > > > > Yes, that boots with no problems. > > > > clickety-clicketa... git blame include/linux/module.h : > > > > commit 7ead8b8313d92b3a69a1a61b0dcbc4cd66c960dc > > Author: Li Zefan <lizf@cn.fujitsu.com> > > Date: Mon Aug 17 16:56:28 2009 +0800 > > > > tracing/events: Add module tracepoints > > > > (Adding Li Zefan in CC) > > > > Two things: > > > > 1) In this commit, most of the tracepoints contain argument with side-effects. > > These do not belong there; they should be moved into TRACE_EVENT macros. > > > > 2) There seem to be a null-pointer bug with > > local_read(__module_ref_addr(module, cpu)) in try_module_get(). This should > > be investigated even if we move the argument to TRACE_EVENT. > > Hi Li, > > Fix this, please? >
While we wait for the sun to move to other time zones, can you check if the following patch fixes your problem ?
module: fix __module_ref_addr()
__module_ref_addr() should use per_cpu_ptr() to obfuscate the pointer (RELOC_HIDE is needed for per cpu pointers).
This non-standard per-cpu pointer use has been introduced by commit 720eba31f47aeade8ec130ca7f4353223c49170f
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> CC: Eric Dumazet <dada1@cosmosbay.com> CC: Rusty Russell <rusty@rustcorp.com.au> --- include/linux/module.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
Index: linux-2.6-lttng/include/linux/module.h =================================================================== --- linux-2.6-lttng.orig/include/linux/module.h 2010-03-23 18:11:14.000000000 -0400 +++ linux-2.6-lttng/include/linux/module.h 2010-03-23 18:14:07.000000000 -0400 @@ -467,7 +467,7 @@ void symbol_put_addr(void *addr); static inline local_t *__module_ref_addr(struct module *mod, int cpu) { #ifdef CONFIG_SMP - return (local_t *) (mod->refptr + per_cpu_offset(cpu)); + return (local_t *) per_cpu_ptr(mod->refptr, cpu); #else return &mod->ref; #endif
> > > Thanks, > > > > Mathieu > > > > > > > > > Arguments with side-effects are not skipped by the jump over disabled > > > > instrumentation. This is why we should do that part within the probe declaration > > > > in the TRACE_EVENT macros. > > > > > > > > But if we find out that the problem really is this argument, then it should be > > > > fixed, because something would be wrong with it (just moving it to TRACE_EVENT > > > > is not a proper solution). > > > > > > > > Thanks, > > > > > > > > Mathieu > > > --- > ~Randy
-- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com
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